This invention relates to non-invasive and continuous measurement of arterial oxygen tension.
Arterial oxygen tension or partial pressure and its changes are phenomena with great significance in several fields of medicine, including anesthesiology, treatment of respiratory diseases, and treatment of prematurely born infants. It is very valuable to know exactly what this tension is and to know it continuously and currently. Invasive techniques, such as the analysis of blood samples may overly weaken the patient and in any event cannot give either current or continuous knowledge. The best and quickest analysis of a blood sample consumes several minutes, especially where the laboratory and the patient are a few minutes apart; it can never provide continuous monitoring.
Attempts to predict or determine arterial oxygen tension indirectly from measured tissue oxygen tension have not heretofore yielded any clinically useful methods. When polarographic oxygen sensors are pressed against tissues, such as the skin, the mucous membranes of the mouth, the cornea, or the bulbar conjunctiva, there is no finite steady-state oxygen tension; instead, the recorded oxygen tension falls rapidly to zero. Even after several years of research and development the non-invasive oximeter, which measures oxyhemoglobin saturation rather than oxygen tension, is still not widely used as a monitoring device. In particular, it does not help monitor hyperoxic states.
The present invention is capable of continuously monitoring arterial oxygen tension. It can measure arterial oxygen tension in both hyperoxic and hypoxic states and is not limited by the 100% saturation of hemoglobin as is the oximeter.
The invention enables an anesthetist to observe the instant effect of decreasing and increasing inspired oxygen tension and ventilation.
When ventilation is assisted in chronic and acute respiratory disease, there is need for evaluating the state of respiration; in addition to data such as tidal volume, blood oxygen tension provided by the present invention can be helpful.
A third immediate area of great usefulness of the present invention is in the premature nursery. For example, isolette oxygen tensions can be adjusted by feedback from a device embodying the invention, chronic palpebral conjunctival electrode taped under one eyelid. Either continuous or sporadic non-invasive, non-blood loss evaluation of arterial PO.sub.2 can be made.
In the area of chronic lung disease a chest internist can use the invention as a diagnostic tool when correlated with certain simple spirometer measurements. In many instances, the non-invasive nature of the test of the present invention is more acceptable on an out-patient basis than arterial puncture.
In the diagnosis and evaluation of shock this invention is capable of greater sensitivity than a sphygmomanometer. The organism tries to maintain its blood pressure and arterial oxygen tension; however, tissue perfusion and oxygenation, especially to non-critical areas, may be affected very easily.